The present invention relates generally to turbomachinery apparatus, and more particularly provides an improved inlet stator vane assembly for use in a turbofan jet engine.
In a typical turbofan engine a core engine is used to drive an axial flow fan which draws ambient air into a main, annular inlet passage, and forces the air through an annular stator vane assembly spanning the inlet passage. The stator vane assembly has a circumferentially spaced series of generally radially extending, airfoil-shaped vanes which are connected between annular inner and outer support shrouds. Inlet air traversing the stator vanes is flow-straightened in the usual manner and then flowed into coannular outer bypass and inner core flow passages having entrances immediately downstream of the vane assembly. Further downstream, the bypass and core flow passages respectively communicate with atmosphere and the core engine inlet.
The stator vane assembly is particularly vulnerable to damage caused by birds or other sizable objects ingested into the main inlet passage during engine operation, such objects having imparted thereto a very high tangential velocity component by the inlet fan. Damage to conventional stator vane assemblies, in turn, can adversely affect subsequent engine performance to an unacceptable degree in one or more of the three following manners.
Perhaps the most serious potential result of stator damage is the breaking away or shattering of vane or shroud structure and ingestion into the core engine of the torn away pieces. This can, of course, seriously damage the many rotating components within the core engine. Another possible form of subsequent engine power loss arising from stator assembly damage is the blockage of the core flow passage by deformed vane and/or support shroud structure. Finally, because of the high tangential velocity component of ingested objects, the potential exists for a single ingested object to cause vane damage around a considerable circumferential portion of the stator vane assembly, drastically reducing the intended flow-straightening capability of the assembly and thus also causing considerable engine power loss.
In the past, a variety of techniques have been employed in an attempt to produce a stator vane assembly which minimizes engine power loss after the vane assembly is struck by an ingested object. None of the resulting vane assemblies has proved entirely satisfactory in this regard.
One conventional stator assembly utilizes rigid solid cast metal vanes to limit vane deformation and the total circumferential extent of vane damage. However, this adds weight to the engine and also increases the chance that one or more vanes will be shattered by ingested objects and drawn into the core engine.
Another approach has been to use bendable vanes fixedly secured between the support shrouds. While this construction tends to solve the vane-shattering problem, the violent bending of the vanes often deforms the inner support shroud, causing blockage of the core flow passage. Additionally, severe bending of the impacted vanes can rip them loose from their support shrouds, sending one or more entire vanes through the core engine.
Yet another previously used vane assembly utilizes bendable vanes which are secured only to the outer support shroud, the inner ends of the vanes being simply extended through suitable openings formed in the inner support shroud so that impacted and bent vanes are merely pulled out of their inner shroud openings. The objective achieved by this design is the reduction inth first two types of engine damage or power loss--the ingestion of stator structure into the core engine and core flow passage blockage. However, it has been found that this reduction in these first two forms of damage substantially increases the third form of damage. The vanes in this type of stator assembly offer comparatively little resistance to the tangential force component of an ingested object, with the result that a single such object can readily render a very large number of vanes aerodynamically inoperable.
From the above it can be seen that there is a need for a stator vane assembly which simultaneously provides protection against each of the three above-described types of stator damage.
Accordingly, it is an object of the present invention to provide a stator vane assembly and associated methods which afford such protection and eliminate or minimize above-mentioned and other problems and disadvantages associated with conventional stator vane assemblies.